In transmissive liquid crystal display devices, to prevent deterioration of switching elements and leak current, light-shielding layers serving as shields against light from backlights are provided in some cases. In liquid crystal display devices used in smartphones and tablet computers, in association with an increase in resolution, there is demand for switching elements which have a smaller size and can pass a larger amount of current. As the method for passing a large amount of current to the switching element, it is known that the gate electrode of the switching element and the light-shielding layer are electrically connected to each other and the light-shielding layer is used as a back gate electrode, for example.
However, in the above-described structure, parasitic capacitance between wires which constitute a pixel increases, and this may cause degradation in display quality.